i need a good nature

[stranger danger]

for chickorita i will be getting one as soon as i evolve 3 pokemon and catch another

 

[WhiteWizard42]

well, it depends on the set, but...

the usual strategy for meganium is leech seed + grasswhistle + leftovers. seedstalling. .... i'd say, depending on whether your attacking move is physical or special (razor leaf, for STAB), you could use either calm or careful.

If you want a more helpful/accurate/relevant answer than that, give the moveset you'll be using.

 

[Spartan 37]

Something to raise the Sp. Atk. maybe. Timid, I believe. But if you're going to use physical attacks as well, I would suggest a neutral personality.

 

[Raden Surya]

Depends from its moveset. If you give me its moveset I can decide the good nature for it.
For me, I use Calm.

 

[Kalosian]

Bold/Calm for a Special one, Impish/Careful for a physical one.

 

[obada]

Go with calm, but you better tell us the moveset.

 

[shauntheiceman]

serebii suggests that you use a chikortia with a adamante nature and using giga drain, bodyslam, toxic and razor leaf

 

[The Organizer]

I think Calm is ideal so you can use all grass and special moves.

 

[WhiteWizard42]

the only special moves chikorita/meganium get are grass-type.

meganium is best suited as a tank, so get a +defense or +special defense nature.

it comes down to, which are you more afraid of? fire and ice, or flying, poison, and bug? fire and ice are more common, so that's why i suggested calm/careful.